Henman, the world No 10, who has overtaken Greg Rusedski in the rankings, beat Koubek 6-1, 6-3, but must wait to see whether he will be invited to the ATP Tour World Championship in Hanover as a replacement after failing to qualify for the eight-man event on merit. If he wins this tournament he will be first replacement for Hanover ahead of the German Tommy Haas and Richard Krajicek of the Netherlands.
"I worked so hard the last two weeks trying to get to Hanover, so I'm disappointed," Henman said of missing an automatic place. "I'm just trying to finish off the season in the best possible way and it's pretty well documented I have not played well enough at the end of the season."
Henman, who meets the American Jan-Michael Gambill in the second round tomorrow, has had his Hanover chances helped by the fact that Pete Sampras and Nicolas Kiefer are unlikely to be fit, while the ninth-placed Marcelo Rios has said he will not play in Germany.
Rusedski, whose season ended prematurely after his injury in Paris last week, has fallen from sixth to 12th place in the new ATP world rankings as well as losing his British No 1 ranking.
Jamie Delgado is top seed at the British National Championships, which start in Telford today. The Berkshire player hopes to take advantage of the absence of Henman and Rusedski to take the title for the first time.